Q: What is the specific rotation $$[\alpha] of a $$solution if the observed rotation is $$-13.9^\circ$$, the concentration is $$0.0548\ \mathrm{g/mL}$$, and the path length is $$1\ \mathrm{dm}$$?

$$[\alpha] = \frac{-13.9^\circ}{0.0548 \times 1} = -253.6^\circ$$

Question 1

Which of the following statements best describes a chiral molecule?

Accepted Answer

A molecule that cannot be superimposed on its mirror image and lacks a plane of symmetry.

Question 2

Which of the following is true about enantiomers?

Accepted Answer

They have identical physical properties except for their interaction with plane-polarized light and other chiral molecules.

Question 3

A molecule with two chiral centers can have a maximum of how many stereoisomers?

Accepted Answer

$$2^2 = 4$

Question 4

Which of the following compounds is achiral?

Accepted Answer

A molecule with a plane of symmetry.

Question 5

Which property is NOT shared by a pair of enantiomers?

Accepted Answer

Direction of rotation of plane-polarized light

Question 6

What is the specific rotation $$[\alpha] of a $$solution if the observed rotation is $$-13.9^\circ$$, the concentration is $$0.0548\ \mathrm{g/mL}$$, and the path length is $$1\ \mathrm{dm}$$?

Accepted Answer

$$[\alpha] = \frac{-13.9^\circ}{0.0548 	imes 1} = -253.6^\circ$$

Question 7

Which of the following best describes a meso compound?

Accepted Answer

A compound with two or more chiral centers and a plane of symmetry.

Question 8

Which of the following is a correct application of the Cahn–Ingold–Prelog priority rules?

Accepted Answer

The group with the highest atomic number attached to the chiral center gets the highest priority.

Question 9

A solution contains 64% (R)-isomer and 36% (S)-isomer. If the observed specific rotation is $$-59.0^\circ$$, what is the specific rotation of the pure (R)-isomer?

Accepted Answer

$$[\alpha] = \frac{-59.0^\circ}{0.28} = -211^\circ$$

Question 10

Which of the following statements about racemic mixtures is correct?

Accepted Answer

They contain equal amounts of both enantiomers and are optically inactive.

Question 11

Which of the following is a real-world consequence of chirality in pharmaceuticals?

Accepted Answer

One enantiomer of a drug may be therapeutically active while the other is inactive or harmful.

Question 12

Which of the following is NOT a stereoisomer?

Accepted Answer

Constitutional isomer

Question 13

Which technique did Louis Pasteur use to separate enantiomers of tartaric acid?

Accepted Answer

Manual separation of mirror-image crystals using tweezers and a microscope.

Question 14

Which of the following best describes a diastereomer?

Accepted Answer

A stereoisomer that is not a mirror image of another stereoisomer.

Question 15

Which of the following statements about Fischer projections is correct?

Accepted Answer

A 180° rotation in the plane of the paper does not change the configuration.

Question 16

Which of the following is a correct statement about optical activity?

Accepted Answer

A racemic mixture is optically inactive because the rotations of the two enantiomers cancel each other.

Question 17

Which of the following is a correct method for separating enantiomers in a racemic mixture?

Accepted Answer

Reacting with a pure chiral compound to form diastereomers, then separating them.

Question 18

Which of the following molecules is chiral?

Accepted Answer

A molecule with a carbon atom bonded to four different groups.

Question 19

Which of the following is true about the relationship between (R)- and (S)-ibuprofen?

Accepted Answer

(S)-ibuprofen is the active enantiomer, while (R)-ibuprofen has diminished activity.

Ch 5: Stereochemistry: Chirality, Isomerism, and Optical Activity

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